[lug] LVM and disk failure

[Daniel Webb]

Thanks for the info, that clears it up some.  What it comes down to, is that
LVM increases flexibility at the price of robustness in the case of a physical
volume failing.  As a result, you want your physical volumes to be *very*
unlikely to fail.  

Absurdum infinitum: suppose you created a volume group out of 1000 RAID-1
pairs.  Now if you put a logical volume spanning the whole volume group, and
one RAID pair dies for whatever reason, the whole thing is gone.  So if N is
the number of physical volumes in your volume group, you should plan for them
to be N times less likely to fail to get the same chance of overall failure as
a single disk.

Also, if you can use the 1000 disks without LVM (maybe you have 1000 files
that just fit each disk), it would be smarter not to use LVM.

But back to part of my original question that wasn't answered: it seems a bit
silly to me that a filesystem is utterly destroyed if you cut it in half;
after all, half of it is still there on the second disk.  A reasonable request
in the name of robustness is that the parts that weren't destroyed should be
recoverable without a huge amount of trouble.  Is that too much to ask?  I
don't really know that much about filesystems, so maybe there are reasons this
is impossible.  And yes, I have seen plenty on recovering ext2 filesystem from
the Google searching to try to answer these questions, it isn't pretty.